Maintaining adequate nitrogen (N) supply to dryland cereal crops remains a critical management issue for optimizing productivity and N-use efficiency. Combinations of crop residue and fertilizer-N inputs can be used to manipulate soil-N supply factors at critical stages of plant N demand. The aim of this study was to understand the effects of residue and N fertilizer combinations on soil-N supply capacity to wheat (Triticum aestivum L.) crop plants under field conditions. Residue decomposition and N release in the field during a fallow period and the subsequent wheat growing season were quantified using litterbags containing wheat or lupin residues placed in the top 1–2 cm of soil. During the growing season, surface (0–10 cm depth) soil-N capacity was assessed in relation to key wheat growth stages by measuring labile organic and inorganic soil-N pools under a combination of different residue (removed, wheat, or lupin residues) and fertilizer-N (0, 20, or 40 kg N ha⁻¹) treatments applied at sowing. Around half of the N release by residues occurred in the fallow period. Lupin residues provided a greater N release via net mineralization and dissolved organic N (DON) early in the growing season (up to tillering). As the crop developed, lupin residues had a higher surface soil potentially mineralizable N (PMN) and microbial biomass N (MBN) compared with wheat or removed residues. It was the combination of lupin residues with fertilizer-N that had the highest overall amount of surface soil DON and PMN between seedling and tillering. This study showed that the fallow is an important component of the N cycle in these systems as 40–50% of crop residue N release occurred during this period. However, this release represented less than 15% of subsequent wheat crop N uptake, which highlights the importance of N cycling from recent residues and pre-existing organic matter during the crop growing season for meeting crop N demand. Lupin residues and fertilizer-N inputs, both independently and together, increased soil-N supply capacity at critical crop growth stages in this low-rainfall sandy soil environment.

为旱地谷类作物保持充足的氮 (N) 供应仍然是优化生产力和氮利用效率的关键管理问题。作物残茬和肥料氮输入的组合可用于在植物氮需求的关键阶段操纵土壤氮供应因素。本研究的目的是了解残留物和氮肥组合对田间条件下小麦 (Triticum aestivum L.) 作物的土壤氮供应能力的影响。在休耕期和随后的小麦生长季节，田间的残留分解和氮释放使用放置在土壤顶部 1-2 厘米处的含有小麦或羽扇豆残留物的垃圾袋进行量化。在生长季节，⁻¹) 播种时应用的处理。大约一半的残留氮释放发生在休耕期。羽扇豆残留物通过生长季节早期（直至分蘖）的净矿化和溶解有机氮 (DON) 提供了更多的氮释放。随着作物的发展，与小麦或去除残留物相比，羽扇豆残留物具有更高的表层土壤潜在矿化氮 (PMN) 和微生物生物量氮 (MBN)。在幼苗和分蘖期间，羽扇豆残留物与肥料-N的组合具有最高的表层土壤DON和PMN总量。该研究表明，休耕是这些系统中氮循环的重要组成部分，因为 40-50% 的作物残留氮释放发生在此期间。然而，这种释放占随后小麦作物氮吸收的不到 15%，这突出了作物生长季节期间近期残留物和预先存在的有机质中的氮循环对于满足作物氮需求的重要性。在这种低降雨量的沙质土壤环境中，羽扇豆残留物和肥料氮投入单独或共同增加了关键作物生长阶段的土壤氮供应能力。